Presently, the mode of supplying spectacle lenses in various countries of the world is broadly classified into two modes.
According to one of the modes, a spectacle shop transmits prescribed values and the kind of lenses to a lens maker's factory or a lens wholesale store to acquire raw lenses not subjected to edging, and the lenses are framed in a selected spectacle frame in the spectacle shop to complete the spectacles. This mode is principally employed in Japan, Southeast Asia, Europe, etc. and is called an uncut mode.
According to the other, an optometrist transmits prescribed values and the kind of lenses and position information of the prescribed values of the lenses in a selected spectacle frame, together with the specific spectacle frame, to a lens maker's factory, and, after production and framing of the lenses in the lens maker's factory, the glazed spectacles are sent back to the optometrist. This mode is principally employed in North America and is called a laboratory mode.
These two modes are frequently employed in parallel. Further, there is a type of spectacle shop which carries specific kinds of lenses although the mode is the uncut mode, and, also, there is a lens factory which carries specific kinds of frames although the mode is the laboratory mode. Thus, there is a case where the aforementioned classification is not necessarily applicable. At least, the laboratory mode differs definitely from the uncut mode in that a lens maker's factory obtains the kind and shape of a selected spectacle frame and can prepare spectacle lenses having a thickness most suitable to that spectacle frame.
This capability of proposing spectacle lenses having a thickness most suitable to a selected spectacle frame is significant chiefly in the case of (+) lenses. As is well knnown, a (+) lens has generally such a shape that it is thickest at the center and becomes progressively thinner toward the periphery thereof. Therefore, when the same peripheral thickness is set for lenses having the same degree, a lens having a larger outer diameter has a larger central thickness. The same applies to spectacle frames, and, generally, a larger spectacle frame requires a thicker lens.
However, in the uncut mode, only a few kinds or, at most, two or three kinds of outer diameters are commonly prepared for lenses of the same diameter and are not enough to closely deal with a variety of kinds of spectacle frames. Therefore, lenses having an outer diameter larger than that required must be used. When, for example, lenses having an original diameter of 60 to 70 mm is subjected to edging until they suit the dimensions and shape of a spectacle frame having an outer shape smaller than the lens diameter, the peripheral thickness (referred to hereinafter as an edge thickness) and the central thickness become larger than the edge thickness of the lenses before being subjected to the edging, in the case of convex lenses. When spectacles are made by such a method, especially, when lenses having a large original outer shape and a spectacle frame having a small size compared with the lenses are used to make spectacles, the glazed spectacles are provided with lenses having a vey large edge thickness and a very large central thickness. Thus, this results in the problem that the glazed spectacles are unnecessarily thick and heavy and also awkward.
As an attempt to correct the above problem as much as possible, there has been proposed a so-called outer-diameter specifying method according to which a spectacle shop measures a required minimum outer diameter of lenses to be mounted in a spectacle frame and specifies that diameter to a lens factory. However, this method is insufficient for application to lenses such as lenses for astigmia, prescribed prism lenses and progressive power ophthalmic lenses having different peripheral thicknesses depending on the direction, although they are circular lenses.
In this respect, according to the laboratory mode as described above, a lens factory obtains the kind and shape of spectacle frames to be used and can produce spectacle lenses having a thickness most suitable for each of the individual spectacle frames. However due to the necessity of the step of transportation of an expensive frame, the laboratory mode involves the additional problem that a great risk such as damage to or loss or mislaying of the frame may be encountered.
Thus, when the shape of a spectacle frame can be measured by a simple and convenient method, and the information thereof can be sent to a lens maker's factory, spectacle lenses conforming to the spectacle frame can be produced.
Methods of measuring the shape of a spectacle frame and applying the measured shape of the spectacle frame as an input includes: (a) a method of measuring the shape of the spectacle frame by a measuring instrument such as a scale and applying the measured numerical valves an an input to a computer; (b) a method of converting the shape of eyepieces by mechanical means or electrical means and applying the converted values as an input to a computer; and (c) a method of using an image scanner of an image pick-up tube.
However, the methods described above have been disadvantageous in that none of them is a method according to which an ordering side (a spectacle shop or the like) obtains conveniently and accurately the shape of a spectacle frame as numerical values approximating the actual shape of the spectacle frame, and permits such numerical values to be applied an an input to a computer and easily read out when so required.